We have extremely exciting evidence from the initial award period of Project 1 that hepatic insulin resistance is the major defect in glucose homeostasis associated with the PCOS susceptibility variant. This variant, allele 8 (A8) of the dinucleotide repeat D19S884, was mapped to intron 55 of the fibrillin-3 gene as part of Project 2 of this SCOR. Male first-degree relatives with the A8 variant have evidence for abnormalities in insulin secretion suggesting that the metabolic phenotypes associated with the A8 variant are sex-specific. The central hypothesis of the NU SCOR is that hyperandrogenemia resulting from variation in a gene(s) regulating steroidogenesis causes the PCOS metabolic phenotype by programming actions at critical periods of development as well as by ongoing actions in the adult. We will plan three Specific Aims: 1. To test the hypothesis that hepatic glucose homeostasis differs by A8 genotype in women with PCOS. Postabsorptive hepatic glucose homeostasis, including rates of gluconeogenesis and glycoge no lysis, will be assessed with state-of-the-art stable isotope techniques. Responses to stimuli that modulate hepatic glucose production, such as glucagon, hypoglycemia and glucose per se, will be examined. 2. To test the hypothesis that androgens alter hepatic glucose homeostasis, directly or by antagonizing estrogen action, in women with PCOS and that this action differs by A8 genotype. The impact of blocking androgen action with the nonsteroidal receptor antagonist, flutamide, alone and during transdermal estradiol replacement, will be investigated. Endpoints will include hepatic and peripheral insulin action as well as any alterations in hepatic glucose homeostasis identified in Aim 1. 3. To test the hypothesis that metabolic phenotypes associated with A8 are sex-specific in the families of women with PCOS. The impact of A8 genotype on hepatic and peripheral insulin action and on insulin secretion will be examined in the brothers of women with PCOS and in age, weight and ethnicity comparable control men. Since hyperandrogenemia appears to be a final common path to the female reproductive phenotype, elucidating the mechanisms for its association with metabolic defects will be relevant to understanding diverse causes of PCOS as well as an important risk factor for type 2 diabetes.